1. Field of the Invention
The present invention relates to workpiece holding devices for machine tools.
2. Description of Related Art
Machine tools, such as lathes, turning centers, milling/turning centers, and the like, are used to remove material from a workpiece. A chuck is often used in such a machine tool to hold the workpiece while the machining operation is being conducted. Generally, a chuck is a workpiece clamp that is operably associated with the machine tool. In most implementations, the chuck is attached to a rotatable spindle of the machine tool. Thus, in such an implementation, the machine tool's spindle rotates the workpiece via the chuck.
Chucks comprise moveable dogs or jaws that engage and hold the workpiece in a fixed relationship to the chuck. Three-jaw chucks are particularly well-suited for holding generally cylindrical parts. Three-jaw chucks typically include jaws that move in unison. In other words, all three jaws are commonly actuated to hold a workpiece or to release a workpiece. Four-jaw chucks typically include jaws that move independently of one another. In other words, each jaw is independently actuated to hold a workpiece or to release a workpiece. Four-jaw chucks are particularly well-suited for holding workpieces that are not generally cylindrical, such as workpieces that are asymmetrical in cross-section. Chucks also exist that have more than four jaws. Such chucks typically include jaws that move independently of one another.
Some workpieces cannot be effectively held by a chuck during machining operations. Many factors are considered when determining whether a particular workpiece can be held by a chuck, such as workpiece complexity, material thickness, dimensional tolerances of the finished part, and the like. Specialized workpiece holding devices are often used to hold workpieces that cannot effectively be held by a chuck. In order to use such specialized workpiece holding devices, however, the chuck must be removed from the machine tool and replaced, generally, with a face plate. The specialized tooling can then be mounted to the face plate.
Removing the chuck and mounting the face plate adds to the time required to setup the machining operation, thus increasing the cost of machining the workpiece. In a machine tool that uses a manually-operated chuck, the chuck is detached from the machine tool's spindle as the chuck is being supported. Once detached from the spindle, the chuck is moved, sometimes with a hoist or the like, to a storage area. The face plate is then picked up from a storage area and moved to the machine tool. If the face plate is heavy, a hoist or the like is used. The face plate is then attached to the spindle. It should be noted that a machine tool produces revenue for the machine tool's owner only when a part is being machined, not during set up operations.
Some machine tools use automated chucks, such as hydraulically-operated chucks. The effort required to remove such a chuck and mount the face plate is increased, and may be dramatically increased, over manually-operated chucks. For example, hydraulic or other such power-providing lines must be removed and possibly drained prior to removing an automated chuck from a machine tool. Moreover, in a hydraulically-operated chuck, if hydraulic fluid is spilled during removal of the hydraulic lines, the spill must be removed to avoid a safety hazard. After the power-providing lines are removed, the chuck is removed and replaced with a face plate, as described above concerning manually-operated chucks.
There are many designs of machine tools and workpiece holding devices well known in the art; however, considerable shortcomings remain.